Emulsion polymers prepared from vinyl esters, particularly those prepared from vinyl acetate and ethylene, have wide application as adhesives and as binders in industry. Unfortunately, these binders sometimes experience unacceptable loss in strength in the presence of water and other solvents. In an attempt to reduce these problems, various crosslinking comonomers and/or post-added crosslinkers have been incorporated into the binders. The most successful of these crosslinkers have been N-methylol acrylamide [NMA] and urea-formaldehyde [U/F] condensates. While the latter are low in cost, compatible with aqueous emulsions and rapidly cured under acid catalysis, their consequent emission of low levels of formaldehyde, a suspect carcinogen, make them undesirable for many applications.
Many attempts have been made to overcome or minimize this deficiency, especially after the potential carcinogenicity and irritant properties of formaldehyde became widely recognized. In this regard many non-formaldehyde containing functional monomers have been added to the emulsion polymers. While many of the functional monomers such as acrylamido glycolic acid and its derivatives have provided acceptable results in acrylate containing emulsions, it has been very difficult to obtain comonomers which would satisfactorily copolymerize with adhesives and binders containing vinyl esters, particularly vinyl acetate. Thus, most of the functional monomers which can readily be incorporated into acrylic emulsion polymers do not yield comparable results in vinyl acetate containing systems since these monomers hydrolyze during emulsion polymerization with the hydrophilic vinyl esters thereby losing their effectiveness.